Devices for measuring superfine particle masses serve to record and/or analyze immissions from aerosols or dusts in general. Of interest first of all in this connection are the purely physical deposition kinetics on particular surfaces (deposition surfaces) by adsorption. Substances can at the same time also diffuse into the surface from the aerosols or dusts, i.e., be taken up and embedded (absorption) as part of a physical diffusion process. It is also possible for chemical and physical interactions of the superfine particles on or in the deposition surfaces to be recorded by these devices and to be quantified by additional morphological, physical or chemical analysis methods of a known type.
An important area of use of the aforementioned devices are also in vitro analyses of fine-dust depositions or of biochemical or biophysical interactions on bioassays, i.e., on biological or biologically active surfaces. Especially in the case of a toxicological assessment of atmospheric dust exposures and atmospheric noxiant exposures, for example, at contaminated work areas, in traffic, or in industrial plants, such analyses are a supplement to epidemiological studies (with statistical data) or in vivo analyses on living individuals (e.g., with animal experiments) that is useful and preferred due to ethical considerations.
Immissions analysis is particularly important in the case of so-called superfine particle exposures. Superfine particles, which also include nanoparticles, refer to particles having diameters below 10 μm, i.e., from a few nanometers to at most one micrometer. Standardized in DIN ISO/TS 27687 are, for example, fine dust (e.g., PM10=particle diameter less than 10 μm) and ultrafine dust. A nanoparticle is therefore a nanoobject having all three outer dimensions on the nanoscale from 1 to 100 nm. Superfine particles, with their very large ratio of surface to mass, often have a property profile and reaction behavior which is completely different compared to larger particles or solid bodies and which has not yet been completely studied and is thus unknown.
DE 100 61 976 A1 describes a device for measuring superfine particle masses comprising an exposure system having a measurement chamber having a deposition surface for particles on a piezoelectric crystal, each deposition surface having an aerosol feed line directed thereto for feeding an aerosol onto the deposition surface.
In vitro investigations relating to the measurement of superfine particle masses and also their toxicological effects on living organisms often utilize biological model structures such as, for example, cell cultures on a corresponding cultivation support structure such as, for example, a Petri dish or, in the case of bacterial cultures, a nutrient medium or membrane culture inserts having pores in relation to the lower compartment. The structures are exposed as open layer to the aerosol or to a suspension of a carrier fluid (gas or liquid) and the superfine particles.
DE 198 01763 C2 describes a culture device for the cultivation of cells or tissue components in which the cell cultures are grown on porous membranes in culture inserts. For the aforementioned in vitro investigations, the nutrient solution on the upper side of the planar cultures is removed for the application of an aerosol, whereas the space below the membrane is continuously flushed with fresh nutrient medium for cell sustenance and to avoid an accumulation of toxic metabolic products. The system has already established itself in many areas of inhalation research such as, for example, for studying diesel soot and cigarette smoke.
EP 1 174 496 A1 also describes a device to cultivate biological cultures having a gaseous fluid on the top side and a liquid on the bottom side combined with a computational dose determination.
The in vitro investigations known to date are, however, solely based on time-integral measurements. The cell cultures are, as are the aforementioned in vivo investigations, only examined at intervals, i.e., only after expiration of a particular test duration. In many cases, fluctuations in an aerosol immission and their temporary biochemical effects on a cell culture cannot be comprehended or can only be comprehended very imprecisely, for example, on the basis of individual tests.
DE 10 2007 013 938 A1 describes a device for measuring superfine particle masses with an exposure system having at least two measurement chambers each having a deposition surface of identical geometries and each having an aerosol feed line directed to the respective deposition surface. The design involves at least one of the deposition surfaces on a piezoelectric crystal as a superfine balance and other deposition surfaces without piezoelectric crystal. An electrical field between aerosol feed line and deposition surface is also proposed to increase the efficiency of deposition. The recommendation is to minimize the difference in electrical potential between any ionized superfine particles in the aerosol and the aerosol feed line.
Cultex Laboratories GmbH, Hanover, also supplies a culture chamber in which an aerosol is charged by a corona on an input side and conducted onto cell cultures with an applied electric potential.
Savi et al. describes a similar concept (Savi M., Kalberer M., Lang D., Ryser M., Fierz M., Gaschen A., Rička J., Geiser M.; A novel exposure system for the efficient and controlled deposition of aerosol particles onto cell cultures; Environmental Science and Technology 42 (2008) 5667-5674) of a passive grid over the deposition surface for the homogenization of the electrical field.
The only currently-known devices are therefore devices to measure superfine particle masses with electrostatic deposition, in which devices the deposition surface is, as the electrode, at a voltage level (for example a high voltage in the kV range). If the deposition surface is provided with a piezoelectric crystal as a superfine balance for a QCM measurement (QCM=Quartz Crystal Microbalance), the superfine balance must disadvantageously also be controlled at the stated voltage level. In relation thereto, the stated voltage level is applied to the above-lying measurement electrode of the piezoelectric crystal and thus corresponds to the potential at the cell culture. So as not to significantly alter the QCM measurement, the principle of which is based on the change in natural frequency in the excited piezoelectric crystal, the necessary voltage difference of a few volts between measurement electrode and the second annular electrode of the piezoelectric crystal should be raised altogther by 1000 volts, i.e., the annular electrode to 1000 volts and the measurement electrode to, for example, 1010 volts. However, the realization of such a concept requires novel oscillators and an inconvenient complex frequency analysis.
Superfine dust or nanoparticles are distinguished by a large specific surface area. This significantly favors a strong adhesion of these particles to planar surfaces, such as the stated deposition surfaces, predominantly by van der Waals forces. Further adhesion mechanisms such as, for example, bondings or surface voltage effects may additionally have an effect, but take a backseat and are negligible in the present case for fine dusts or nanoparticles.